Belled End Fittings - Surve Jitendra.

Create a spark to reduce labor, welding costs

For 70 years, factory-made, wrought butt-welding fittings were the choice for pressure piping systems, in shapes defined by ASME B16.9. However, in recent years, new metal forming processes have enabled the development of wrought socket-welding fittings.

By Ray Stubbs Jr., Bestweld Inc. -- Plant Engineering, 6/15/2008

For 70 years, factory-made, wrought butt-welding fittings were the choice for pressure piping systems, in shapes defined by ASME B16.9. However, in recent years, new metal forming processes have enabled the development of wrought socket-welding fittings. In 1996, those fittings were standardized in “MSS Standard Practice SP-119, Belled End Socket Welding Fittings, Stainless Steel and Copper Nickel” – more familiarly known as “belled-end pipe fittings.” The bodies of these are essentially the same as those in ASME B16.9, but the welding skill, materials and labor time to join them are far less extensive.

According to the American Welding Society and the Bureau of Export Administration, in their May 2002 report entitled Welding Related Expenditures, Investments and Productivity Measurement in U.S. Manufacturing, Construction and Mining Industries, labor typically accounts for 76% of total welding cost. Given the amount of welding involved in a typical piping system, simplifying the process can amount to considerable savings.

This simple change in pipe fitting specification can save 50% to 70% of the labor time needed in joint preparation and welding. Multiply that by each joint throughout the piping system, and this can amount to huge savings to the plant budget. And while significant economic advantages are realized, no sacrifice is made in piping system performance – and in some cases system reliability is improved.

Easing the fit and the weld

Cold-formed, wrought belled-end pipe fittings have expanded ends, creating a socket to receive the connecting pipe. This design allows them to be joined by fillet welds rather than the butt welds needed to join traditional pipe fittings. Both the type of weld and the shape of the parts make good welds easier to achieve.

Fillet welds can be done four to seven times faster and require fewer steps than butt welds. Much less joint preparation goes into a fillet weld, with no machining of parts onsite needed to ensure fit. Butt-welded joints require both pieces to be beveled at the point of installation for a precise fit of root geometry.

Pre-weld fit time is virtually eliminated with belled-end fittings, where butt-welded joints take a significant amount of time to fit. Belled-end fittings joined with fillet welds are more forgiving: where the shape and alignment of the two pieces may vary just a slight amount, welds can still be done successfully. With butt-welding, “out of round” situations, misalignment and mismatched wall thicknesses can cause problems in achieving a good weld.

In butt-welding, an interior backing ring may sometimes be needed to support the welded seam and provide a good surface on which to weld the two beveled edges together. The backing ring is tacked in place, and then weld material is deposited into the groove created by the two machined parts. Where a backing ring is not used, the two parts still must be fit into a jig and tack-weld before being final-welded into place. Joining belled-end fittings with fillet welds eliminates these preliminary steps. In addition, back-side weld joint gas inerting is often required for butt joints but is seldom needed for socket welds.

The ability to use a fillet weld at a lap joint between the fitting and the pipe instead of a butt weld also reduces the chance for burn through – a contributor to internal deformities such as craters, fissures and icicles that can affect process flow. Fillet welds are much easier to do and much less expensive to inspect. Most fillet welds are accomplished in one root pass and one finish pass, whereas comparable strength butt-welded joints require multiple passes. Fillet welds are inspected visually for size and slope, but butt welds are inspected radiographically in order to ensure proper joint preparation and root pass penetration.

Belled-end fittings perform

Today, B31.3, the piping designer’s most significant specification, recognizes the MSS SP119 fillet weld fittings as a cost-reducing alternative to standard butt welding fittings. The current edition of ASME B31 Code for Pressure Piping lays out design requirements for effective, safe and insurable systems. B31.3 Process Piping is “piping typically found in petroleum refineries, chemical, pharmaceutical, textile, paper, semiconductor and cryogenic plants, and related processing plants and terminals.”

But how does performance stack up? Fillet welds in themselves are strong, reliable joints; in piping systems using belled-end pipe fittings, the performance meets or exceeds standard pipe fittings. The fittings provide the same pressure and temperature limits as the corresponding butt-weld fittings. Manufacturers’ design-proof burst testing confirms that MSS-SP119 fittings have burst capacities matching those of ASME B16.9 rated butt-welded fittings.

The fillet-welded joint is stronger than the pipe alone. The cold-formed wrought fittings also better match the wall thicknesses of piping systems than cast or forged fittings, which tend to be rigid and oversized. That properly enables systems with belled-end fittings to flex more uniformly, distributing the stress into the sidewalls rather than the joints. This extends system life where fatigue is a concern.

U.S. Navy testing of the fittings discovered that the fitting bell contributed a significant reinforcement value to elbows. In fatigue testing of angular displacement large enough to produce B16.9 elbow failures in 1,000 cycles, belled-end elbow fittings lasted two to four times longer, the testing found.

Belled end fittings have Piping Code recognition: the current standard MSS SP-119 is referenced by B31.3, Code for Chemical Piping. Standard Practice SP-119 currently is being revised to include belled-end fittings in more materials and with thicker walls, broadening the application possibilities.

Belled end fittings can be used with standard wall and light wall pipe, and commonly are supplied in several alloys of stainless steel, copper nickel, titanium and aluminum. In today’s economy, labor cost outweighs component cost; even where special materials are used, installation and performance issues still make belled-end fittings a preferred choice.

Consideration of welding requirements during piping design will yield impressive benefits. Using belled-end fittings can help a manufacturing facility cut welding labor costs, reduce inspection costs and welding rework and build stronger piping systems.

---

Author Information

Ray Stubbs has been in the welded piping industry for more than 30 years, serving since 1984 as a founding partner and vice president of sales at Bestweld Inc. A producer of stainless steel and higher nickel alloy welding fittings for high-pressure, high-temperature and severe corrosion applications, Bestweld is a U.S. Navy ship parts supplier. Bestweld was named 2004 Supplier of the Year by Northrop Grumman Newport News and Northrop Grumman Ship Systems.

 

Use of fittings can help combat the loss of skilled welders Choosing belled-end pipe fittings also can help plants address a major problem in industry today: the lack of highly skilled welders. Besides enabling faster production of good joints, belled-end pipe fittings benefit plant engineering departments because less advanced welding skills are needed than for comparable strength, butt-welded systems. As experienced welders retire, a broad range of welding knowledge is leaving the workplace. New graduates show low interest in welding, while technology creates more uses for the skill. In a May 2002 survey by the American Welding Society and The Bureau of Export Administration, almost 50% of companies studied said the numbers of their welding trainees were not adequate to meet replacement requirements. More than 40% of heavy industrial manufacturing firms indicated that a shortage of qualified welders affects productivity either “moderately” or “extensively,” and approximately 30% of the firms in the automotive and construction industrial sectors indicated similar levels of impact, the survey indicated. Lack of skilled welders also can inhibit manufacturing expansion plans, affecting the economy as a whole. Welders with advanced skills command premium wages. According to an August 2006 Wall Street Journal report, graduates of welding technical programs can receive annual salaries in excess of $50,000. By specifying belled-end pipe fittings, the productivity of welding professionals, whether on staff or outside, can be maximized and costs can be minimized.

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Pipe Span Factors - a note by Hassan Hajitabar.

In general Pipe span is limited by pipe material (allowable stress),
sectional modulus (nominal size and Sch. of pipe) and weight of its content
and insulation and design temperature of the pipe system which affects
allowable stress in calculation of pipe span. In general pipe span is
limited by allowable deflection and allowable bending and shear stress. To
simplify pipe support spacing calculation MSS- SP69 has provided recommended
practice for support spacing which has been accepted by ASME. These spans
are limited to max. combined stress(bending and shear) to 1500 PSI and max.
pipe sag of 0.1 inch we use allowable pipe span as a general and primary
solution for supporting but some points should be considered in supporting:
1- All span should be adjusted based on available structure for supporting.
2- In case of change of direction in horizontal pipes you should reduce pipe
span. as a good practice you can use 0.75 of span.
3- Span should be decreased based on concentrated weight and load in piping
system such as valve and flange. As a good practice you can use 0.75 of span
for one element and 0.6 of span for two elements in piping system.
4- finally you should consider maintenance requirement(for example for valve
maintenance and removal) you should consider supports as possible as near to
valves).
Also I should note hear that occasional loads such as wind and earthquake do
not concern span of weight support because using span is used for dead
loads. For this loads stress analyzer engineer should use proper guide and
other dynamic supports such as rigid strut and shock absorber with careful
attention to thermal expansion and load.
When you see various recommended span for a same size it may means using of
various safety factor, various fluid content, various design temp. Various
pipe materials and other design objects in calculation of max. allowable
span.

In general we have:

L < (10 * Z* F * S/W)^0.5
In which
L= Max. allowable span(mm)
Z= Pipe sectional modulus(mm3)
F= Safety factor
S=Allowable stress in design temp(N/mm2).
W=Weight per linear unit of pipe(N/mm)
I hope these all are useful for you.

Best Regards
Hassan Hajitabar

Piping Engineer
Engineering Department
Iranian Offshore Engineering & Construction Company (IOEC)
E-mail: Hajitabar@Ioec.com

A 197 cupola malleable iron.(The missing picture)

A 197 cupola malleable iron.

"Bathula Raghuram \(Mumbai - PIPING\)" <r.bathula@ticb.com> Sent by: piping_valves@yahoogroups.com 17/06/2008 13:02 Please respond to piping_valves@yahoogroups.com

To <piping_valves@yahoogroups.com> cc Subject RE: [piping_valves] A 197 cupola malleable iron.

Cupola malleable iron is a blackheart malleable iron that is produced by cupola melting and is used for pipe fittings (probably in ANSI G49.1 I think) and similar thin-section castings.

 

The essential purpose of melting is to produce molten iron of the desired composition and temperature. For gray iron, this can be accomplished with various types of melting equipment. Cupolas and induction furnaces tend to be the types most commonly found in the gray iron foundry. The cupola was traditionally the major source of molten iron. However, gradual acceptance of electric melting has reduced the dominance of the cupola.

 

The following are the Grades of malleable iron specified according to minimum tensile properties (Source: ASM Handbook)

 

 Jitendra Surve Wrote:

Please enlighten me with your analysis of Cupola malleable iron A 197.
 
It seems to have low carbon content for malleability.
 
 
Regards,
Jitendra

Autofrettage of piping

The subject is more familiar to Stress engineers. Thought of sharing the basics with others.

The link below gives the basics behind the Autofrettage.
http://www.interlaken.com/legacysite/pdf/Autofrettage_ABCs.pdf

Though widely popular in other industries, in petrochemical field, the lines subject to high pressure piping such as LLDPE plants of Borestar technology of Borealis and LDPE of Lupotech technology of Basell have very high pressure piping which are in most cases licensor engineered items. General recommendation in such piping is to ensure that the piping does not fail under fatique loads. To arrive the pre compression stress equivalent autofrettage pressure limit, the pipe is analysed and plotted for various thickness percentage segments and how the stresses peak and drop, so that to arrive the optimum residual stress and the equivalent autofrettage pressure.

The pipe and fittings are subject to that resultant pressure and pre stressed before installation. Thus it is ensured that the piping can withstand higher fatigue loads and shock pressures of very high pressure services. Also observe the various stress curves on the attached snap of a sample analysis.

Stress engineers in the group are requested to share more of thier experience and views.

With regards,
Kannan.

Fugitive emission in valves [Second part]

In continuation of the subject, also look into the uploaded files on the subjects by Piet de Later of Dow chemicals.

http://tech.groups.yahoo.com/group/piping_valves/files/

Secondly,  this regulation is to have strict control and leak resistance on the hazardous emission of dust, steam or gas happening due to the external leakages for the safety reasons and long term reliability of the valves.

For instance: Cd, Hg, Ti, CO, NOx  < 0.2 mg/m3.
                   As, Co, Ni, Se             < 1.0 mg/m3.
                   Pb, Sb, F, CN           < 5.0 mg/m3.

For ball valves max. leakage rates of 0.03 g.h-1 are allowed for substances involving a risk potential. The maximum emission rate of He = 4.99x10-2 bars cm3s-1 is deemed to be permissible after a 100,000 operational cycles with Helium test medium at room temperature under a 55 bars pressure. This could be achieved for example, by means of specific design of packing or by means of bellows and a subsequent safety stuffing bushing and with PTFE sealing, if permitted for the service condition.

With regards,
Kannan.

17-4PH cracking.

People involved in the valve application, take care before placing order to know the component materials of the valve. The 17-4PH usually used in the stem construction have failed like the below. Tyco valves has observed similar failures in thier inhouse research and has reported the same on using 17-4PH. And are not recommending this material unless specifically asked for.

As all suppliers and buyers do not take much interest in the small components of the valve, it will be the responsibility of the buyer to take note of these before ordering and the complete knowledge of the service involved. Alternatives would be FXM19, F51, F6a Cl4 depending on temp. and service.(17-4PH is 17Cr-4Ni-Pricipatation Hardened)

http://www.hghouston.com/x/25.html

(Photo attached for members not having net access.)



Nomarski intereference contrast photograph of the microstructure of a 17-4PH stainless steel sleeve bearing overlayed with sintered tungsten carbide. A hydrogen embrittlement crack has initiated at the overlay/base metal interface. A mechanical crack in the overlay permitted access of a corrosive downhole environment to the 17-4PH stainless steel base metal. Vilellla's etch. (~65X)

With regards,
Kannan.

Fugitive emission in valves.

Ta-Luft - Technical instruction on air quality directive item 5.2.6. VDI 2440, has set the creteria under which leakage rate the packing of valve (any type) can be accepted using helium as the medium for the test. Helium has been choosen as it is the best inert gas and excellent sensors are availabe to smell it. The creteria also includes the application temp. range.

The test can be performed only once on the prototype design of the packing in the presence of a TPI like TUV inspector. And they witness and issue the certificate which can be accepted by a purchaser as a base reference for a type of valve, particular size range and temp. range for that design of packing or a spectrum of different designs of packing.

Now coming to your question, by packing I mean the stem packing of any valve. This act Ta-Luft was enacted to reduce the fugitive emmision of the plant. Most of the valve packing are degraded after certain cylces of operation and the service starts leaking. The Ta-Luft mentioned above is for only valve packing and includes the no. of cycle of operation where mechanical arrangement during testing, strokes the valve stem from close to open position automatically with a counter.

There are other Ta-Luft laws which dictates many other different type of emmisions other than the valve packing.

Helium leak test specific to individual manufacturer's own standard, as such is not accepted in the current market. Widely  accepted are the Ta-Luft and the Shell's SPE 77/312 which calls for more stringent creteria as the individual manufacturer's testing procedure are not much reliable without any reference scale.

Just for your information, nowadays most of the well known manufacturer's have adapted the Ta-Luft as a default design and offer it, even if you don't call for it.

Though this law is applicable only for Germany, it has been informally adapted by most of the European and Asian country plant owners. In USA the equivalent law is Called as Clean Air act. The approach is different in the testing and creteria but the end result emmision is slightly less stringent than the Ta-Luft requirements. The more stringent to follow is the Shell SPE 77/312. BP in US has its own standard like the shell in line with Clean Air act.

VDI is like the Institution of Engineers of India of Germany, The association of German Engineers but very active and creactive group having strong lobby in the government even today, which is responsible in bringing the Ta-Luft law more than two decades back well before the Clean Air act.

With regards,
Kannan
Linde, Germany.

**********************************************
http://piping-valves.blogspot.com/
http://materials-welding.blogspot.com/
**********************************************

Sandesh Mane wrote:
 
Just a query...
Where are the low emmission valve used and is it related only to stem packing or some other design criteria is also there.
 
Do all low emission valves shall be helium leak tested /TALUF certified....
 
what is difference between taluf cert valves and helium leak test ??...which one is more stringent.
 
regards,
Sandesh Mane

What is Galvanizing...?

What is corrosion?
How do you protect iron and steel from corrosion?
How do you galvanize?
Surface PreparationGalvanizing Inspection
What is the resulting metallurgical bond?
Service Life Expectations for Galvanized Steel


What is corrosion?
Corrosion is the reaction between a material and its environment that produces a deterioration of the material and alters its mechanical properties. The actual corrosion process that takes place on a piece of bare mild steel is very complex due to factors such as variations in the composition/structure of the steel, presence of impurities due to the higher instance of recycled steel, uneven internal stress, or exposure to a non-uniform environment.
It is very easy for microscopic areas of the exposed metal to become relatively anodic or cathodic. A large number of such areas can develop in a small section of the exposed metal. Further, it is highly possible that several different types of galvanic corrosion cells are present in the same small area of the actively corroding piece of steel.
As the corrosion process progresses, the electrolyte may change due to materials dissolving in or precipitating from the solution. Additionally, corrosion products might tend to build up on certain areas of the metal. These corrosion products do not occupy the same position in the given galvanic series as the metallic component of their constituent element. As time goes by, there may be a change in the location of relatively cathodic or anodic areas and previously uncorroded areas of the metal are attacked and corrode. This eventually will result in uniform corrosion of the area.
The rate at which metals corrode is controlled by factors such as electrical potential and resistance between anodic and cathodic areas, pH of the electrolyte, temperature and humidity.
How do you protect iron and steel from corrosion?
Barrier protection is perhaps the oldest and most widely used method of corrosion protection. It acts by isolating the metal from the electrolytes in the environment. Two important properties of barrier protection are adhesion to the base metal and abrasion resistance.
Cathodic protection is an equally important method for preventing corrosion. Cathodic protection requires changing an element of the corrosion circuit, introducing a new corrosion element, and ensuring that the base metal becomes the cathodic element of the circuit. Hot-dip galvanizing provides excellent barrier and cathodic protection. The sacrificial anode method, in which a metal or alloy that is anodic to the metal to be protected is placed in the circuit and becomes the anode. The protected metal becomes the cathode and does not corrode. The anode corrodes, thereby providing the desired sacrificial protection. In nearly all electrolytes encountered in everyday use, zinc is anodic to iron and steel. Thus, the galvanized coating provides cathodic corrosion protection as well as barrier protection.




How do you galvanize?
The galvanizing process consists of three basic steps: surface preparation, galvanizing and inspection.




Surface Preparation
Surface Preparation is the most important step in the application of any coating. In most instances where a coating fails before the end of its expected service life, it is due to incorrect or inadequate surface preparation.
The surface preparation step in the galvanizing process has its own built-in means of quality control in that zinc simply will not react with a steel surface that is not perfectly clean. Any failures or inadequacies in surface preparation will be immediately apparent when the steel is withdrawn from the molten zinc. Any areas that were not properly prepared will remain uncoated. Immediate corrective action is taken.
Surface preparation for galvanizing typically consists of three steps: caustic cleaning, acid pickling and fluxing.
Caustic Cleaning – A hot alkali solution often is used to remove organic contaminants such as dirt, paint markings, grease and oil from the metal surface. Epoxies, vinyls, asphalt or welding slag must be removed before galvanizing by grit-blasting, sandblasting or other mechanical means.
Pickling – Scale and rust normally are removed from the steel surface by pickling in a dilute solution of hot sulfuric acid or ambient temperature hydrochloric acid.
Fluxing – Fluxing is the final surface preparation step in the galvanizing process. Fluxing removes oxides and prevents further oxides from forming on the surface of the metal prior to galvanizing and promotes bonding of the zinc to the steel or iron surface. The method for applying the flux depends upon whether the particular galvanizing plant uses the wet or dry galvanizing process.
In the dry galvanizing process, the steel or iron materials are dipped or pre-fluxed in an aqueous solution of zinc ammonium chloride. The material is then thoroughly dried prior to immersion in molten zinc.




Galvanizing
In this step, the material is completely immersed in a bath consisting of a minimum 98% pure molten zinc. The bath chemistry is specified by the American Society for Testing and Materials (ASTM) in Specification B 6. The bath temperature is maintained at about 850 F (454 C).
Fabricated items are immersed in the bath long enough to reach bath temperature. The articles are withdrawn slowly from the galvanizing bath and the excess zinc is removed by draining, vibrating and/or centrifuging.
The chemical reactions that result in the formation and structure of the galvanized coating continue after the articles are withdrawn from the bath as long as these articles are near the bath temperature. The articles are cooled in either water or ambient air immediately after withdrawal from the bath.




Inspection
The two properties of the hot-dip galvanized coating that are closely scrutinized after galvanizing are coating thickness and coating appearance. A variety of simple physical and laboratory tests may be performed to determine thickness, uniformity, adherence and appearance.
Products are galvanized according to long-established, well-accepted and approved standards of the ASTM, the Canadian Standards Association (CSA), and the American Association of State Highway and Transportation Officials (AASHTO). These standards cover everything from the minimum required coating thicknesses for various categories of galvanized items to the composition of the zinc metal used in the process.




What is the resulting metallurgical bond?
Galvanizing forms a metallurgical bond between the zinc and the underlying steel or iron, creating a barrier that is part of the metal itself. During galvanizing the molten zinc reacts with the surface of the steel or iron article to form a series of zinc/iron alloy layers. The photomicrograph below shows a typical galvanized coating microstructure consisting of three alloy layers and a layer of pure metallic zinc. Moving from the underlying steel surface outward, these are:
The thin Gamma layer composed of an alloy that is 75% zinc and 25% iron,
The Delta layer composed of an alloy that is 90% zinc and 10% iron,
The Zeta layer composed of an alloy that is 94% zinc and 6% iron, and
The outer Eta layer that is composed of pure zinc.




































Service Life Expectations for Galvanized Steel
The graph below is a plot of the thickness of the galvanized coating against the expected service life of the galvanized coating under outdoor exposure conditions. Most galvanized applications are 4 mils of thickness minimum per surface.
The expected service life is defined as the life until 5% of the surface is showing iron oxide (rust). At this stage, it is unlikely that the underlying steel or iron has been weakened or the integrity of the structures protected by the galvanized coating otherwise compromised through corrosion.




Graph – “Life of Protection”


















Painting Over Hot-Dip Galvanized Steel
For years, protecting steel from corrosion typically involved either the use of hot dip galvanizing or some type of paint system. However, more and more corrosion specialists are utilizing both methods of corrosion protection in what is commonly referred to as a duplex system. A duplex system is simply painting or powder coating steel that has been hot dip galvanized after fabrication. When paint and galvanized steel are used together, the corrosion protection is superior to either protection system used alone.

Painting galvanized steel requires careful preparation and a good understanding of both painting and galvanizing. Many products have been galvanized and painted successfully for decades, including automobiles and utility towers. Past experience provides excellent historical data for how best to achieve good adhesion. By studying past adhesion failures and successes, galvanizers, paint companies, researchers, paint contractors, and other sources have created an ASTM specification detailing the process and procedures for preparing hot dip galvanized steel for painting. When the galvanized surface is prepared correctly, paint adhesion is excellent and the duplex system becomes an even more successful method of corrosion protection.

How a Duplex System Works
Before deciding how to protect steel from corrosion, it is important to understand how steel corrodes. Corrosion of steel takes place because of differences in electrical potential between small areas on the steel surface which become anodic and cathodic. When an electrolyte connects the anodes to the cathodes, a corrosion cell is created. Moisture in the air forming condensation on the steel surface is the most common electrolyte. In the electrolyte, a small electrical current begins to flow. The iron ions produced at the anode combine with the environment to form the loose, flaky iron oxide known as rust.In order to protect steel from corrosion, something must interfere with the corrosion cell, either by blocking the electrolyte or becoming the anode. Two common methods of corrosion protection are cathodic protection (the fonnation of another anode) and barrier protection (blocking the electrolyte from the steel surface). Hot dip galvanizing alone affords both types of protection.

Aging Characteristics of Galvanized Coatings
Galvanized steel can be divided into three categories: newly galvanized steel, partially weathered galvanized steel and fully weathered galvanized steel. Each type of galvanized steel must be prepared slightly different because the galvanized surface has different characteristics at each stage of weathering. It is important to know the age of the galvanized steel that will be painted.

Newly Galvanized Steel
Newly galvanized steel is zinccoated steel which has been hot dip galvanized after fabrication within the past 48 hours. The newly galvanized steel should not be water or chromate quenched, nor should it be oiled. This type of galvanized surface is typically very smooth and the surface may need to be slightly roughened, using one of the profiling methods described in this publication, to improve paint adhesion. A newly galvanized surface has little or no zinc oxides or zinc hydroxides, so no major cleaning is necessary.

Partially Weathered Galvanized Steel
Partially weathered galvanized steel has begun to form the protective zinc patina, but has not completed the process. Before painting partially weathered galvanized steel, it is important to know if the coating was chromate quenched. The presence of chromateconversion coatings can be determined by spot testing the galvanized steel according to ASTM B 201. If a chromate coating is detected the chromate layer must be removed, either by brushing off by abrasive blast cleaning, abrading the steel by sanding or allowing the steel to weather for six months.
Partially weathered galvanized steel should also be inspected for wet storage stain. Since wet storage stain is hygroscopic and has a larger volume than the zinc metal, paint adhesion can be seriously affected when this stain is painted. Wet storage stain is a whitish zinc corrosion byproduct. If the surface to be painted has wet storage stain, it should be carefully removed by brushing the stain with a mild ammonia solution, such as diluted household ammonia. Severe cases of wet storage stain should be brushed with a mild acidic solution, such as one part acetic acid mixed with 25 parts water. Follow these cleaning procedures with a clean, warm water rinse.
Partially weathered galvanized steel also should be slightly roughened to improve paint adhesion. Any of the surface profiling methods described in this publication can be used to prepare the surface.

Fully Weathered Galvanized Steel
Fully weathered galvanized steel has a completely formed zinc patina. The patina has a very stable and finely etched surface, which provides excellent paint adhesion. The only surface preparation needed is a warm water power wash to remove loose particles from the surface. In order to protect the surface, the power wash should not exceed 1450 psi. Allow the surface to completely dry before application of the paint system.

Profiling
In order to provide a good adhesion profile for the paint, the galvanized surface must be flat with no protrusions and slightly roughened to provide an anchor profile for the paint system. Filing high spots, sweep blasting, phosphating, and using wash primers or acrylic passivations are the most common methods of increasing the profile of a galvanized surface. Again, care must be taken not to damage the galvanized coating.

High Spots
Any high spots or rough edges should be removed and smoothed out in order to provide a level surface for paint. Use hand or power tools to grind down the high spots. Care should be taken to remove as little zinc as possible.

Sweep Blasting
In order to roughen the typically smooth galvanized surface after cleaning, an abrasive sweep or brush blast may be used. Care should be taken to prevent removing too much of the zinc coating. Particle size for a sweep blast of galvanized steel should range between 200 and 500 microns (8 to 20 mils). Aluminum/magnesium silicate has been used successfully in the sweep blasting of galvanized steel. Organic media such as corn cobs, walnut shells, corundum, limestone, and mineral sands with a Mobs hardness of five or less may also be used. The temperature of the galvanized part when blasting can have a Significant affect on the finished surface profile. Sweep blasting while the galvanized part is still warm, 175 to 390 degrees F, provides an excellent profile. Ambient conditions for sweep blasting are recommended to be less than 50 percent relative humidity and a minimum of 70 degrees F.

Repair of Damaged Galvanized Surfaces
Sometimes hot-dip galvanized coatings are damaged by excessively rough handling during shipping or erection. Welding or flame cutting may also result in coating damage.
When limited areas are damaged, the use of low melting-point zinc alloy repair rods or powders, the use of organic zinc-rich paints or metallizing is recommended to protect the area.
We would like to express our appreciation to The American Galvanizing Association for supplying material and photographs for our web site.
For additional information on the topics listed above please contact The American Galvanizing Association or Ben Pletcher, Sales Manager, Ohio Galvanizing Corp.

Specifications
The primary specification that government organizations, engineering firms, specifiers, and fabricators desire is ASTM A123. This specification is defined by the American Society for Testing and Materials. Items such as coating thickness, guidelines for acceptance, and testing methods are documented.
Additional specifications for areas such as the galvanizing of steel hardware and fasteners (ASTM A153) and the allowable practices for repair of galvanized steel (ASTM A7890) are also listed.
A 123
Standard for Specification of Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products
A 153
Standard for Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware
A 780
Standard for Specification for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings
Ohio Galvanizing is a member of the American Galvanizing Association and galvanizes all material to the ASTM A123 specification. We will provide the proper documentation for those jobs requiring certification to the specifications of ASTM A123.

With regards,
Kannan.

One reason for Inner ring and outer ring in Spiral wound gaskets.

As everybody know that in spiral wound gasket the outer ring is meant to be as a centering ring for assembly and is being called for by default. The inner ring is to remove the potential for the spot weld joint on the spiral ring to corrode or crack leading to the metallic spiral ring unwinding. The result of this failure may cause an obstruction in the pipe bore, breakdown of the gasket and ultimately reduce the sealing integrity of the joint. So it is advisable to prescribe SPW gaskets with inner and outer rings of suitable material compatable with the service in category M as prescribed in B31.3.

With regards,
Kannan.
Linde, Germany.